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Author Topic: Importance of pollution and clouds in the Arctic  (Read 1070 times)

LRC1962

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Importance of pollution and clouds in the Arctic
« on: January 06, 2018, 07:33:07 AM »
Clouds that are more 'sensitive' to pollution are speeding up Arctic warming
Quote
"Climate models show a difference between 2 C and 6 C," Taylor said. "The reason that difference is so large is because of cloud cover."
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A-Team

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Re: Importance of pollution and clouds in the Arctic
« Reply #1 on: January 06, 2018, 03:38:54 PM »
Some interesting remarks in the article, notably about the irrelevance of biomass burning to radiative properties of Arctic clouds. (Note algal surface growth, not so much soot, seems behind Greenland darkening). It's all about plume tracks and their dilution with distance: hypothetical reductions in Asian pollutants may well be offset by increased Arctic shipping emissions.

The article addresses 2005-10 and does not provide any products relevant to predicting cloud contribution to the current freeze or melt seasons.

High Sensitivity of Arctic Liquid Clouds to Long-Range Anthropogenic Aerosol Transport
Q. Coopman, TJ Garrett et al
3 Jan 2018 DOI: 10.1002/2017GL075795

The rate of warming in the Arctic depends upon the response of low-level microphysical and radiative cloud properties to aerosols advected from distant anthropogenic and biomass-burning sources. Cloud droplet cross-section density increases with higher concentrations of cloud condensation nuclei, leading to an increase of cloud droplet absorption and scattering radiative cross sections. The challenge of assessing the magnitude of the effect has been decoupling the aerosol impacts on clouds from how clouds change solely due to natural meteorological variability.

Here we address this issue with large, multi-year satellite, meteorological, and tracer transport model data sets to show that the response of low-level clouds in the Arctic to anthropogenic aerosols lies close to a theoretical maximum and is between 2 and 8 times higher than has been observed elsewhere. However, a previously described response of arctic clouds to biomass-burning plumes appears to be overstated because the interactions are rare and modification of cloud radiative properties appears better explained by coincident changes in temperature, humidity, and atmospheric stability.

Increased concentrations of cloud condensation nuclei (CCN) cause cloud droplets to become more numerous and, for constant liquid water content, this leads to smaller droplets and higher radiative cross-section densities.

The radiative impacts of CCN are important enough to potentially lead to a warmer surface and accelerated melting of arctic sea ice, particularly in winter and spring when the longwave response dominates and pollution levels are high.

The last decade has seen a lengthening and intensification of boreal forest fires that has led to increased biomass-burning (BB) aerosol concentrations in the Arctic, a trend that is expected to continue.

On the other hand, a downward trend in mid-latitude anthropogenic (ANT) emissions has lowered concentrations of arctic sulphur although this may be offset by future Arctic industrialization and shipping.

Assessment of the impact of these aerosol changes on arctic clouds has been a challenge because surface and airborne observations in the Arctic are sparse, aerosol compositions are regionally varied and complex, and both aerosol transport and cloud formation are determined by meteorological conditions, in particular by the humidity, temperature, and lower tropospheric stability (LTS).

Our study aims to robustly isolate how lower-latitude ANT and BB aerosols affect clouds over the Arctic, independent of local meteorological changes. For maximum coverage, we use space-based data sets for the retrieval of low-level liquid cloud properties, and we quantify the magnitude of aerosol-cloud interactions (ACI) by vertically and horizontally colocating clouds with pollution concentrations from numerical tracer transport model output for the Arctic for a period between March and September for the years 2005 to 2010.

Here we looked at the sensitivity ACInet of arctic clouds to passive pollution plumes from distant sources rather than the sensitivity to local aerosols ACI. Precipitation can remove aerosols during long-range transport and therefore decrease the value of ACInet relative to ACI. We find that observed values of ACInet for anthropogenic pollution plumes already lie close to a theoretical maximum value of 0.33, implying that values of ACI are either similar or not significantly higher. N

Arctic clouds are more susceptible to pollution plumes than other regions. It cannot be explained by the low concentration of aerosols because the logarithm of the ACInet already take into account this effect. A hypothesis is the favorable condition of the Arctic region with high LTS. It is possible that values of ACI are particularly high in the Arctic due to elevated LTS and a reduced potential for vertical mixing with sub-saturated air. In less stable mid-latitude regions, mixing processes decrease the sensitivity of clouds to aerosols by enhancing droplet evaporation.

Regardless of the precise mechanisms, the implication of the measurements is that arctic climate may be particularly sensitive to any future changes in anthropogenic pollution concentrations. Determining the effect of aerosol-cloud interactions on surface temperatures is complicated by the unique physics of the region: increasing ? not only brightens clouds but can also lead to a higher longwave cloud emissivity; either a significant net warming or cooling occurs depending on ? , the season, and the coverage of sea-ice.

In the future, a combination of reductions in emissions of mid-latitude pollutants and increased wet scavenging in a warmer climate is anticipated to reduce the arctic aerosol burden by 61.0% by the end of the century. Based on the ACI values found here, this can be expected to correspond to an 18% decrease in ? , but with a possible compensating increase due to increasing arctic maritime transportation and industrialization. A further consideration is that the dynamic response of cloud amount to aerosols is itself a function of aerosols and meteorological conditions.The ultimate climate impact remains to be determined.

Air in the Arctic is extraordinarily sensitive to air pollution, and that particulate matter may spur Arctic cloud formation. These clouds, Garrett writes, can act as a blanket, further warming an already-changing Arctic.

"The Arctic climate is delicate, just as the ecosystems present there," T Garrett says. "The clouds are right at the edge of their existence and they have a big impact on local climate. It looks like clouds there are especially sensitive to air pollution. Early Arctic explorers' notes show that air pollution has been traveling northward for nearly 150 years or more. This pollution would naturally get blown northward because that's the dominant circulation pattern to move from lower latitudes toward the poles," he says. Once in the Arctic, the pollution becomes trapped under a temperature inversion, preventing the accumulated bad air from escaping.

Which regions contribute to Arctic pollution? Northeast Asia is a significant contributor. So are sources in the far north of Europe. They have far more direct access to the Arctic. Pollution sources there don't get diluted throughout the atmosphere."

Scientists have been interested in the effects of pollution on Arctic clouds because of their potential warming effect. In other parts of the world, clouds can cool the surface because their white color reflects solar energy back out into space. "In the Arctic, the cooling effect isn't as large because the sea-ice at the surface is already bright," Garrett says. "Just as clouds reflect radiation efficiently, they also absorb radiation efficiently and re-emit that energy back to warm the surface." Droplets of water can form around particulate matter in the air. More particles make for more droplets, which makes for a cloud that warms the surface more.

Satellite images can detect aerosol pollution in the air -- but not through clouds. "We'll look at the clouds at one place and hope that the aerosols nearby are representative of the aerosols where the cloud is," says Garrett. "They're not going to be. The cloud is there because it's in a different meteorological air mass than where the clear sky is."

So Garrett and his colleagues, including U graduate Quentin Coopman, needed a different approach. Atmospheric models, it turns out, do a good job of tracking the movements of air pollution around the Earth.

Using global inventories of pollution sources, they simulate air pollution plumes so that satellites can observe what happens when these modeled plumes interact with Arctic clouds. The model allowed the researchers to study air pollution and clouds at the same time and place and also take into account the meteorological conditions. They could be sure the effects they were seeing weren't just natural meteorological variations in normal cloud-forming conditions.

The research team found that clouds in the Arctic were two to eight times more sensitive to air pollution than clouds at other latitudes. They don't know for sure why yet, but hypothesize it may have to do with the stillness of the Arctic air mass. Without the air turbulence seen at mid-latitudes, the Arctic air can be easily perturbed by airborne particulates.

One factor the clouds were not sensitive to, however, was smoke from forest fires. "It's not that forest fires don't have the potential," Garrett says, "it's just that the plumes from these fires didn't end up in the same place as clouds."

Air pollution attributable to human activities exceeded the influence of forest fires on Arctic clouds by a factor of around 100:1.

Particulate matter is an airborne pollutant that can be controlled relatively easily, compared to pollutants like carbon dioxide. Controlling current particulate matter sources could ease pollution in the Arctic, decrease cloud cover, and slow down warming.

All of those gains could be offset if the Arctic becomes a shipping route and sees industrialization and development. Emissions from those activities could have a disproportionate effect on Arctic clouds compared to emissions from other parts of the world, Garrett says.

"The Arctic is changing incredibly rapidly," he says. "Much more rapidly than the rest of the world, which is changing rapidly enough."
« Last Edit: January 06, 2018, 03:45:46 PM by A-Team »

jai mitchell

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Re: Importance of pollution and clouds in the Arctic
« Reply #2 on: January 06, 2018, 07:50:49 PM »
While increasing the temperature of the arctic during the winter months, the observation of clouds as a suppressor of temperature and ice loss rates during the summer melting season is well documented.  The increase (2 to 8 times) of arctic cloud impacts compared to  midlatitude clouds as a result of Asian pollution shows that our current melt regime is being stalled by these emissions.

I have recently observed a large change in the temperature trends between the satellite and land-based series.  This large shift is unprecedented in the satellite monitoring period.  This even began around June of 2017. 

Concurrent to this unprecedented shift was a major change in the trajectory of the ENSO away from the return of a strong El Nino and back to a La Nina.  This process has been identified in models to also be an indication of a large pulse of increased pollution.

My reference post with the graphs can be found here:  https://forum.arctic-sea-ice.net/index.php/topic,1225.msg137892.html#msg137892

I also note that the PIOMAS data posted by A-Team also shows a rapid reduction in the rate of sea ice loss about this time, further indicating the potential for large increases of pollution at this time and its global impacts on the climate.
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Stephan

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Re: Importance of pollution and clouds in the Arctic
« Reply #3 on: April 24, 2018, 08:52:16 PM »
I just post here some latest news about the pollution of the Arctic with microplastic particles:
http://www.tagesschau.de/ausland/mikroplastik-arktis-101.html (sorry it is in German, but the original article in "Nature Communications" can probably be easily found).
While reading this I asked myself whether these zillions of particles may have an effect on the ice formation (the freezing point might be reduced ??) or the albedo of the ice body itself (if no snow cover is on top of it), apart from the effects on marine life and the whole eco system.
I myself have never asked for a plastic bag in a shop for at least twenty years as I always carry a bag or a backpack with me.

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